In the medical field, for diagnosis of various diseases and examination of progress of the condition of a disease, measurement of the content of a protein distinctive to a disease existing in a human bodily fluid is widely conducted. For the measurement of the content of a protein, immunoreaction measurement methods, mainly utilizing reaction of an antibody specifically recognizing a target protein as an antigen (antigen-antibody reaction), is in widespread use. At present, immunoreaction measurement methods utilizing various principles have been developed.
Among others, measurement methods such as immunonephelometry, immunoturbidimetry and slide agglutination are well known, in which agglutinates of antigen-antibody complexes (hereinafter, simply called agglutinate complexes) formed by antigen-antibody reaction are detected. These measurement methods are employed in the state that an antigen and an antibody are dispersed uniformly in a solution, which are therefore collectively called “homogeneous immunoreaction measurement methods”.
In the antigen-antibody reaction, the reaction system becomes turbid with formation of agglutinate complexes. The degree of turbidity generated in the reaction system with formation of agglutinate complexes depends on the amount of the antigen and the amount of the antibody. Immunonephelometry and immunoturbidimetry are methods utilizing this fact, in which the degree of turbidity generated in the reaction system is optically measured and the amount of the antigen or the amount of the antibody is computed from the measured value.
The degree of turbidity generated in the reaction system is measured based on the amount of light scattered in the reaction system for immunonephelometry, or based on the amount of transmitted light decreasing due to scattering in the reaction system for immunoturbidimetry. In general, the same reaction system can be used for measurement by immunonephelometry and measurement by immunoturbidimetry. In other words, a reaction system usable for measurement by either immunonephelometry or immunoturbidimetry can be used for measurement by the other method. Slide agglutination is a method in which a solution in a reaction system having turbidity is collected on a glass slide or the like and the degree of turbidity in the reaction system is determined by visual observation and the like. The same reaction system as that used for immunonephelometry and immunoturbidimetry can be used for the slide agglutination method.